1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for managing a backup channel in a multi-channel environment.
2. Discussion of the Related Art
In a Cognitive Radio (CR) network, when a priority order user appears, an operating channel has to be conceded to the priority order user, and the operating channel has to be switched. Candidate channels for switching the operating channel are managed. A list of the candidate channels is called a backup channel. The backup channel is generated on the basis of information about whether there is a user in a corresponding channel based on sensing or DB information and information about whether the corresponding channel is available.
In order to send data over a CR network, a CR device does not use one transmission method, but optimizes and uses a transmission method according to a channel condition. The CR device may send data in accordance with a Single Input Single Output (SISO) method using a single antenna, a Multiple Input Multiple Output (MIMO) method using multiple antennas, or using one or more channels at the same time. Furthermore, data may be transmitted by changing modulation methods, such as QPSK, 16 QAM, and 64 QAM.
Quality information about a backup channel generated using a sense function or DB information informs whether each channel is available, but does not inform the transmission quality of the corresponding channel. Communication channels may have different transmission qualities according to a method of sending data or modulation methods, or every channel or every transmission/reception terminal. In other words, a CR device trying to send a radio frame using a channel has to send the radio frame by adjusting a transmission method or a modulation method or both according to the state of the corresponding channel. For example, in the case where a channel state is good when a modulation method to be used is determined, the radio frame may be transmitted by raising a modulation order.
In the case where a priority order user appears in a channel now being operated and a channel has to be switched to a backup channel, there may be a problem in that requirements of service already being served are not satisfied owing to the channel switching because the transmission quality of the channel now being operated differs from the transmission quality of the previous backup channel.
For example, assuming that a CR device using multiple antennas supports both the MIMO transmission method and the SISO transmission method, the MIMO transmission method and the SISO transmission method have not only different maximum transmission rates, but also different transmission qualities according to each channel. Accordingly, in the case where the operating channel of a CR device sending data in a specific channel according to the MIMO transmission method switches to another channel, there is a case where a transmission quality provided in the previous specific channel according to the MIMO transmission method does not remain intact in the switched another channel.
Furthermore, the transmission quality varies per channel, per time, and the location of a terminal. In a CR network in which the switching of a channel is generated during operation, not only the transmission quality of an operating channel, but also the transmission quality of a backup channel to switch has to be taken into consideration when the channel is switched. If channel switching is performed by not taking the transmission quality into consideration, there may be a problem in that Quality of Service (QoS) of data already being served is not satisfied until the transmission quality of a moved channel is determined. Furthermore, there is a time delay problem until a transmission method has to be adjusted by measuring the transmission quality of the moved channel.
Accordingly, not only a backup channel is configured and managed on the basis of only information about whether a channel is available, but also information about the transmission quality of a generated backup channel has to be further managed. In order to solve the problem, a method and apparatus for managing a backup channel in a multi-channel environment needs to be taken into consideration.